Dynamic countdown of remaining characters in a cell? Possible?

Hi Guys,

I'd like to have a dynamic countdown of characters within a cell. Is this possible? I'm thinking it's not as when text is being entered the cell will be in edit mode and no calculations will take place. Hoping it is possible though.

Failing that I was going to use LEN and possibly conditional formatting to highlight to the user what range of chars they might have left.

Any other suggestions?

Many thanks.

thank you. Heres to hoping someone knows how to do it with VBA